Organic electroluminescent devices

ABSTRACT

An OLED structure including a first organic layer disposed between the anode and the cathode is disclosed. The first organic layer includes a primary phosphorescent emitter and a first host, and where one of the following conditions is true: (1) the first organic layer further includes a secondary emitter; or (2) the OLED further includes a second organic layer disposed between the anode and the cathode, wherein the second organic layer includes a secondary emitter. The phosphorescent emitter has a peak emission wavelength λmax that is ≥600 nm and ≤750 nm, the secondary emitter has a peak emission wavelength λmax that is ≥750 nm, and the first host has a lowest excited state triplet energy T1 that is at least 0.1 eV higher than that of the primary phosphorescent emitter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application No. 62/582,359, filed Nov. 7, 2017, the entirecontents of which are incorporated herein by reference.

FIELD

The present invention relates to organic light emitting diodes.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting diodes/devices (OLEDs), organic phototransistors, organicphotovoltaic cells, and organic photodetectors. For OLEDs, the organicmaterials may have performance advantages over conventional materials.For example, the wavelength at which an organic emissive layer emitslight may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Alternatively the OLED can be designed to emit white light. Inconventional liquid crystal displays emission from a white backlight isfiltered using absorption filters to produce red, green and blueemission. The same technique can also be used with OLEDs. The white OLEDcan be either a single EML device or a stack structure. Color may bemeasured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processable” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative) Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY

Near-infrared (NIR) OLEDs may have a number of applications includingimaging, night vision, and medical therapies. While making use ofphosphorescence in OLEDs offers a mechanism for greatly improving deviceefficiencies, fluorescent emitters and lanthanide based emitters mayoffer some unique advantages in the regime of NIR energy excitons suchas shorter excited state lifetimes, higher emission quantum yields, andnarrow lineshape emission.

In order to combine the efficiency benefit of phosphorescent OLEDmaterials with the advantages of other emitters, we add to aphosphorescent OLED device structure a secondary NIR emitter wherein theprimary phosphorescent emitter acts as a sensitizer to the secondary NIRemitter. The secondary NIR emitter can be a lanthanide complex, anorganic fluorophore or a doublet emitter. In this configuration, theemissive layer (EML) of the phosphorescent OLED having a primaryphosphorescent emitter dopant may be uniformly or non-uniformly(gradient, bands of varied concentration, etc.) co-doped with thesecondary NIR emitter. Alternatively, the secondary NIR emitter can beprovided as a separate discrete layer within or adjacent to the EML towhich energy transfer may occur.

An OLED comprising an anode, a cathode, and a first organic layerdisposed between the anode and the cathode is disclosed. The firstorganic layer comprises a primary phosphorescent emitter and a firsthost, and where one of the following conditions is true: (1) the firstorganic layer further comprises a secondary emitter; or (2) the OLEDfurther comprises a second organic layer disposed between the anode andthe cathode, where the second organic comprises a secondary emitter. Thephosphorescent emitter has a peak emission wavelength λmax that is ≥600nm and ≤750 nm. The secondary emitter has a peak emission wavelengthλmax that is ≥750 nm. The first host has a lowest excited state tripletenergy T1 that is at least 0.1 eV higher than that of the phosphorescentemitter.

A consumer product comprising the OLED is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are schematic and the structures in the drawings do notrepresent dimensions to scale.

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows an example OLED stack incorporating separate emissivelayers to physically separate the primary and secondary emitters.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), are incorporated byreference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink jet and organic vaporjet printing (OVJP). Other methods may also be used. The materials to bedeposited may be modified to make them compatible with a particulardeposition method. For example, substituents such as alkyl and arylgroups, branched or unbranched, and preferably containing at least 3carbons, may be used in small molecules to enhance their ability toundergo solution processing. Substituents having 20 carbons or more maybe used, and 3-20 carbons is a preferred range. Materials withasymmetric structures may have better solution processability than thosehaving symmetric structures, because asymmetric materials may have alower tendency to recrystallize. Dendrimer substituents may be used toenhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. A consumer product comprising an OLED thatincludes the compound of the present disclosure in the organic layer inthe OLED is disclosed. Such consumer products would include any kind ofproducts that include one or more light source(s) and/or one or more ofsome type of visual displays. Some examples of such consumer productsinclude flat panel displays, curved displays, computer monitors, medicalmonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads-up displays, fully or partiallytransparent displays, flexible displays, rollable displays, foldabledisplays, stretchable displays, laser printers, telephones, mobilephones, tablets, phablets, personal digital assistants (PDAs), wearabledevices, laptop computers, digital cameras, camcorders, viewfinders,micro-displays (displays that are less than 2 inches diagonal), 3-Ddisplays, virtual reality or augmented reality displays, vehicles, videowalls comprising multiple displays tiled together, theater or stadiumscreen, a light therapy device, and a sign. Various control mechanismsmay be used to control devices fabricated in accordance with the presentinvention, including passive matrix and active matrix. Many of thedevices are intended for use in a temperature range comfortable tohumans, such as 18 degrees C. to 30 degrees C., and more preferably atroom temperature (20-25 degrees C.), but could be used outside thistemperature range, for example, from −40 degree C. to +80 degree C.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms “halo,” “halogen,” or “halide” as used interchangeably andrefer to fluorine, chlorine, bromine, and iodine.

The term “acyl” refers to a substituted carbonyl radical (C(O)—R_(s)).

The term “ester” refers to a substituted oxycarbonyl (—OC(O)—R_(s) or—C(O)—O—R_(s)) radical.

The term “ether” refers to an —OR_(s) radical.

The terms “sulfanyl” or “thio-ether” are used interchangeably and referto a —SR_(s) radical.

The term “sulfinyl” refers to a —S(O)—R_(s) radical.

The term “sulfonyl” refers to a —SO₂—R_(s) radical.

The term “phosphino” refers to a —P(R_(s))₃ radical, wherein each R_(s)can be same or different.

The term “silyl” refers to a —Si(R_(s))₃ radical, wherein each R_(s) canbe same or different.

In each of the above, R_(s) can be hydrogen or a substituent selectedfrom the group consisting of deuterium, halogen, alkyl, cycloalkyl,heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl,alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, andcombination thereof. Preferred R_(s) is selected from the groupconsisting of alkyl, cycloalkyl, aryl, heteroaryl, and combinationthereof.

The term “alkyl” refers to and includes both straight and branched chainalkyl radicals. Preferred alkyl groups are those containing from one tofifteen carbon atoms and includes methyl, ethyl, propyl, 1-methylethyl,butyl, 1-methylpropyl, 2-methylpropyl, pentyl, 1-methylbutyl,2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,2,2-dimethylpropyl, and the like. Additionally, the alkyl group may beoptionally substituted.

The term “cycloalkyl” refers to and includes monocyclic, polycyclic, andspiro alkyl radicals. Preferred cycloalkyl groups are those containing 3to 12 ring carbon atoms and includes cyclopropyl, cyclopentyl,cyclohexyl, bicyclo[3.1.1]heptyl, spiro[4.5]decyl, spiro[5.5]undecyl,adamantyl, and the like. Additionally, the cycloalkyl group may beoptionally substituted.

The terms “heteroalkyl” or “heterocycloalkyl” refer to an alkyl or acycloalkyl radical, respectively, having at least one carbon atomreplaced by a heteroatom. Optionally the at least one heteroatom isselected from O, S, N, P, B, Si and Se, preferably, O, S or N.Additionally, the heteroalkyl or heterocycloalkyl group is optionallysubstituted.

The term “alkenyl” refers to and includes both straight and branchedchain alkene radicals. Alkenyl groups are essentially alkyl groups thatinclude at least one carbon-carbon double bond in the alkyl chain.Cycloalkenyl groups are essentially cycloalkyl groups that include atleast one carbon-carbon double bond in the cycloalkyl ring. The term“heteroalkenyl” as used herein refers to an alkenyl radical having atleast one carbon atom replaced by a heteroatom. Optionally the at leastone heteroatom is selected from O, S, N, P, B, Si and Se, preferably, O,S or N. Preferred alkenyl, cycloalkenyl, or heteroalkenyl groups arethose containing two to fifteen carbon atoms. Additionally, the alkenyl,cycloalkenyl, or heteroalkenyl group is optionally substituted.

The term “alkynyl” refers to and includes both straight and branchedchain alkyne radicals. Preferred alkynyl groups are those containing twoto fifteen carbon atoms. Additionally, the alkynyl group is optionallysubstituted.

The terms “aralkyl” or “arylalkyl” are used interchangeably and refer toan alkyl group that is substituted with an aryl group. Additionally, thearalkyl group is optionally substituted.

The term “heterocyclic group” refers to and includes aromatic andnon-aromatic cyclic radicals containing at least one heteroatom.Optionally the at least one heteroatom is selected from O, S, N, P, B,Si and Se, preferably, O, S or N. Hetero-aromatic cyclic radicals may beused interchangeably with heteroaryl. Preferred hetero-non-aromaticcyclic groups are those containing 3 to 7 ring atoms which includes atleast one hetero atom, and includes cyclic amines such as morpholino,piperidino, pyrrolidino, and the like, and cyclic ethers/thio-ethers,such as tetrahydrofuran, tetrahydropyran, tetrahydrothiophene, and thelike. Additionally, the heterocyclic group may be optionallysubstituted.

The term “aryl” refers to and includes both single-ring aromatichydrocarbyl groups and polycyclic aromatic ring systems. The polycyclicrings may have two or more rings in which two carbons are common to twoadjoining rings (the rings are “fused”) wherein at least one of therings is an aromatic hydrocarbyl group, e.g., the other rings can becycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls.Preferred aryl groups are those containing six to thirty carbon atoms,preferably six to twenty carbon atoms, more preferably six to twelvecarbon atoms. Especially preferred is an aryl group having six carbons,ten carbons or twelve carbons. Suitable aryl groups include phenyl,biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene,anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene,perylene, and azulene, preferably phenyl, biphenyl, triphenyl,triphenylene, fluorene, and naphthalene. Additionally, the aryl group isoptionally substituted.

The term “heteroaryl” refers to and includes both single-ringhetero-aromatic groups and polycyclic aromatic ring systems that includeat least one heteroatom. The heteroatoms include, but are not limited toO, S, N, P, B, Si and Se. In many instances, O, S or N are the preferredheteroatoms. Hetero-single ring aromatic systems are preferably singlerings with 5 or 6 ring atoms, and the ring can have from one to sixheteroatoms. The hetero-polycyclic ring systems can have two or morerings in which two atoms are common to two adjoining rings (the ringsare “fused”) wherein at least one of the rings is a heteroaryl, e.g.,the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles,and/or heteroaryls. The hetero-polycyclic aromatic ring systems can havefrom one to six heteroatoms per ring of the polycyclic aromatic ringsystem. Preferred heteroaryl groups are those containing three to thirtycarbon atoms, preferably three to twenty carbon atoms, more preferablythree to twelve carbon atoms. Suitable heteroaryl groups includedibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene,benzofuran, benzothiophene, benzoselenophene, carbazole,indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole,triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole,thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine,oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole,indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline,isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine,phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine,phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine,preferably dibenzothiophene, dibenzofuran, dibenzoselenophene,carbazole, indolocarbazole, imidazole, pyridine, triazine,benzimidazole, 1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine,and aza-analogs thereof. Additionally, the heteroaryl group may beoptionally substituted.

Of the aryl and heteroaryl groups listed above, the groups oftriphenylene, naphthalene, anthracene, dibenzothiophene, dibenzofuran,dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine,pyrazine, pyrimidine, triazine, and benzimidazole, and the respectiveaza-analogs of each thereof are of particular interest.

The terms alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aralkyl, heterocyclic group, aryl,and heteroaryl, as used herein, are independently unsubstituted orsubstituted with one or more general substituents.

In many instances, the general substituents are selected from the groupconsisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile,sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In some instances, the preferred general substituents are selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl,heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, andcombinations thereof.

In some instances, the preferred general substituents are selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl, alkoxy,aryloxy, amino, silyl, aryl, heteroaryl, sulfanyl, and combinationsthereof.

In yet other instances, the more preferred general substituents areselected from the group consisting of deuterium, fluorine, alkyl,cycloalkyl, aryl, heteroaryl, and combinations thereof.

The terms “substituted” and “substitution” refer to a substituent otherthan H that is bonded to the relevant position, e.g., a carbon ornitrogen. For example, when R¹ represents mono-substitution, then one R¹must be other than H (i.e., a substitution). Similarly, when R¹represents di-substitution, then two of R¹ must be other than H.Similarly, when R¹ represents no substitution, R′, for example, can be ahydrogen for available valencies of ring atoms, as in carbon atoms forbenzene and the nitrogen atom in pyrrole, or simply represents nothingfor ring atoms with fully filled valencies, e.g., the nitrogen atom inpyridine. The maximum number of substitutions possible in a ringstructure will depend on the total number of available valencies in thering atoms.

As used herein, “combinations thereof” indicates that one or moremembers of the applicable list are combined to form a known orchemically stable arrangement that one of ordinary skill in the art canenvision from the applicable list. For example, an alkyl and deuteriumcan be combined to form a partial or fully deuterated alkyl group; ahalogen and alkyl can be combined to form a halogenated alkylsubstituent; and a halogen, alkyl, and aryl can be combined to form ahalogenated arylalkyl. In one instance, the term substitution includes acombination of two to four of the listed groups. In another instance,the term substitution includes a combination of two to three groups. Inyet another instance, the term substitution includes a combination oftwo groups. Preferred combinations of substituent groups are those thatcontain up to fifty atoms that are not hydrogen or deuterium, or thosewhich include up to forty atoms that are not hydrogen or deuterium, orthose that include up to thirty atoms that are not hydrogen ordeuterium. In many instances, a preferred combination of substituentgroups will include up to twenty atoms that are not hydrogen ordeuterium.

The “aza” designation in the fragments described herein, i.e.aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more ofthe C—H groups in the respective fragment can be replaced by a nitrogenatom, for example, and without any limitation, azatriphenyleneencompasses both dibenzo[f,h]quinoxaline and dibenzo[f,h]quinoline. Oneof ordinary skill in the art can readily envision other nitrogen analogsof the aza-derivatives described above, and all such analogs areintended to be encompassed by the terms as set forth herein.

As used herein, “deuterium” refers to an isotope of hydrogen. Deuteratedcompounds can be readily prepared using methods known in the art. Forexample, U.S. Pat. No. 8,557,400, Patent Pub. No. WO 2006/095951, andU.S. Pat. Application Pub. No. US 2011/0037057, which are herebyincorporated by reference in their entireties, describe the making ofdeuterium-substituted organometallic complexes. Further reference ismade to Ming Yan, et al., Tetrahedron 2015, 71, 1425-30 and Atzrodt etal., Angew. Chem. Int. Ed. (Reviews) 2007, 46, 7744-65, which areincorporated by reference in their entireties, describe the deuterationof the methylene hydrogens in benzyl amines and efficient pathways toreplace aromatic ring hydrogens with deuterium, respectively.

It is to be understood that when a molecular fragment is described asbeing a substituent or otherwise attached to another moiety, its namemay be written as if it were a fragment (e.g. phenyl, phenylene,naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g.benzene, naphthalene, dibenzofuran). As used herein, these differentways of designating a substituent or attached fragment are considered tobe equivalent.

In the OLED disclosed herein, the organometallic based primaryphosphorescent emitter acts as a charge trap and thus a preferentialsite for the formation of excitons. These excitons then transfer theirenergy to the secondary NIR emitter by either Forster or Dexter energytransfer, depending on the emission mode of the secondary NIR emitter.

When the secondary NIR emitter is comprised of a lanthanide ligand fieldemitter, direct Dexter energy transfer from the primary phosphorrecentemitter to the ligand and/or the f-orbitals of the lanthanide complexultimately results in a lanthanide f-orbital centered exciton which mayact as the effective emission state. In this OLED structure, the energytransfer of the primary phosphor exciton to the secondary NIR emittermust be an energetically favorable process. As such, the primaryphosphorescent emitter may have an excited state energy in the visible,preferably in the red (600 nm≤λ_(max)≤750 nm), range.

More specifically, regarding the case where the secondary NIR emitter isa lanthanide compound, and the emissive layer comprises at least threecomponents including host material(s), the first transition metalphosphorescent compounds (M¹L¹ _(n)) as the primary phosphorescentemitter, and the second transition metal compounds (M²L² _(n)) as thesecondary NIR emitter. The first metal M¹ is selected from a groupconsisting of Os, Ir, Pd, Pt, Cu, Ag, and Au and the second metal M² isselected from lanthanide elements. The first transition metalphosphorscent compound will have a lowest triplet excited state energyT1 that is equal to or higher in energy than the energy of the emissivef-f transition, E_((f-f)), of the second transition metal compound. Theexciton formed on the first transition metal compound will transferenergy, most likely through a Dexter process, forming the excited stateof the second transition metal compound. This device architectureenables a complete or near complete energy transfer from the primaryemitter to the secondary NIR emitter. The lanthanide compound, thesecond transition metal compound, acts as the emitter in the OLEDdevice.

The energy of the emissive f-f transition, E_((f-f)), of the lanthanidecompounds are shown in Table 1. In the last column of Table 1, the f-ftransition energy is given in nms which is also the emission wavelength.

TABLE 1 f-f transition Ln metal Excited state Final state E_((f-f)) (eV)E_((f-f)) (nm) Gd ⁶P_(7/2) ⁸S_(7/2) 3.97 312 Tb ⁵D₄ ⁷F₆ 2.25 551 Dy⁴F_(9/2) ⁶H_(3/2) 2.18 569 Sm ⁴G_(5/2) ⁶H_(5/2) 2.10 590 Eu ⁵D₀ ⁷F₀ 2.02614 Ho ⁵F₅ ⁵I₈ 1.28 969 Yb ²F_(5/2) ²F_(7/2) 1.22 1016 Nd ⁴F_(3/2)⁴I_(11/2) 1.17 1060 Pr ¹G₄ ³H₆ 0.95 1305 Er ⁴I_(13/2) ⁴I_(15/2) 0.811531

When the secondary NIR emitter is comprised of a NIR fluorophore (suchas cyanine, phthalocyanine, porphyrin, rhodamine or other classes of NIRemitters) the primary phosphor must preferably transfer its energy tothe secondary NIR emitter via Forster energy transfer to avoidpopulating the fluorophore triplet state which would result in wastednon-emissive excited states. This condition requires the optimization of(i) the spectral overlap between the emission spectrum of the primaryphosphorescent emitter and the absorption spectrum of the secondary NIRemitter and (ii) steric (molecular) and/or device optimization of thebinary emitter system to prevent unwanted Dexter energy transfer.

In most cases, the spectral overlap condition of the primaryphosphorescent emitter and the secondary NIR emitter would require a redphosphorescent emitter for the primary phosphorescent emitter. Asecondary NIR (fluorescent) emitter with a relatively small (<50 nm)Stokes shift, such as a cyanine dye, with an absorption λ_(max) between750 nm and 850 nm and absorption tailing into the red (600-650 nm) isexpected to be appropriately matched with a red phosphorescent emitter(emission λ_(max) in this regime) for efficient Forster energy transfer.However, for any given NIR emitter the primary phosphorescent redemitter may require optimization for efficient energy transfer. It ispreferred that the primary phosphorescent emitter emission λ_(max) beshifted from the secondary NIR emitter's absorption λ_(max) by less than200 nm, and more preferably less than 150 nm.

In the case of a fluorescent emitter as the secondary NIR emitter,additional molecular and/or device precautions may need to be taken toavoid Dexter energy transfer in order to prevent detrimental formationof fluorophore triplet excitons. Such precautions may include largebulky substituents (iso-propyl, neo-pentyl, tert-butyl, adamantyl, etc)on either primary or secondary emitter to increase primary-to-secondaryemitter distance and minimize wavefunction overlap necessary for Dexterenergy transfer. Such bulky substituents are particularly useful on thesecondary NIR emitter so as to not disrupt charge transport, voltage,and other device properties of the EML and to electronically isolate thesecondary NIR emitter from the EML system. Bulky substituents may beparticularly impactful in preventing Dexter energy transfer when addeddirectly to the π-system of the emitter so as to prevent π-orbitaloverlap.

As the rate of Dexter energy transfer is proportional to e^(−r) where ris the donor-acceptor radius (the distance between two adjacent aprimary phosphorescent emitter to a secondary NIR emitter, in thiscase), this process may also be mitigated by decreased doping of thesecondary NIR emitter or selective doping of the secondary NIR emitteraway from the charge recombination zone (e.g. preferentially on ETL sideof EML). These device structures would increase effective emitterdistance and reduce the rate of unwanted Dexter energy transfer.

Decreasing the rate of Dexter energy transfer through physicallyseparating the two emitters can be achieved through three strategies:(A) spatially isolating the primary and secondary emitters byrestricting the emitters to separate layers during device fabrication;(B) judicious choice of emitter doping percentages or concentrations tostatistically minimize the probability of the primary and secondaryemitters being within the Dexter energy transfer radius; and (C) byintroducing enough non-conjugated steric bulk to one or both of theemitters to sterically prevent the emitters from being within the Dexterenergy transfer radius.

In case (A), the physical separation arises from the inclusion of theprimary and secondary emitters in different layers of the device. Here,the two emissive layers (one containing the primary phosphorescentemitter material and the other containing the secondary NIR emittermaterial) are separated by one or more layers of host or transportmaterials to achieve an interlayer separation distance of greater than 1nm, more preferably greater than 2 nm, and more preferably greater than4 nm.

In cases (B) and (C), the primary and secondary emitters are doped inthe same layer and the physical separation between the primary andsecondary emitters can be described by the distance between the aromaticλ-systems of the two emitters, i.e. the donor-acceptor radius r. Inorder to minimize Dexter energy transfer, r is preferably greater than 8Å, more preferably greater than 10 Å, and more preferably greater than12 Å.

In case (C), where this is achieved by controlling the composition of aco-doped layer, the distance, r, should be predominantly governed by theconcentration of the most abundant of the two dopants. Assuming auniform distribution of dopants within the host matrix and a hexagonalclose packed structure, the concentration of both dopants should be lessthan 10%, more preferably less than 5%, and more preferably less than3%. It is also advantageous to have one dopant less abundant than themajority dopant.

In case (C), where the intramolecular separation arises from pendantsteric bulk on one or both dopants, the spacing afforded by the stericbulk can be roughly described by the difference in distance from thedopant's center of mass to: (a) the farthest aromatic carbon orheteroatom in the dopant; and (b) the farthest non-aromatic atom in thedopant. When only one of the two dopants has this pendant steric bulk,this difference in radial distances, d, is representative of theinter-molecular distance afforded by the bulk. When both dopants havependant steric bulk, the intermolecular distance is roughly equal to thesum d₁+d₂, wherein d₁ is the difference in distance from the firstdopant's center of mass to (a) and (b), and d₂ is the difference indistance from the second dopant's center of mass to (a) and (b). Inorder to prevent Dexter energy transfer, d or d₁+d₂ should be greaterthan 8 Å, more preferably greater than 10 Å, and more preferably greaterthan 12 Å.

In the case of a secondary NIR emitter wherein the excited state is aspin ½ doublet state, energy transfer to this emitter may proceedthrough either Dexter or Forster mechanisms as the doublet emitter doesnot suffer from the formation of exciton states with spin-forbiddenemission. As such, a doublet emitter may be included in a devicestructure that promotes either Dexter or Forster energy transfer.

An OLED comprising an anode, a cathode, and a first organic layerdisposed between the anode and the cathode is disclosed. The firstorganic layer comprises a primary phosphorescent emitter and a firsthost, and where one of the following conditions is true: (1) the firstorganic layer further comprises a secondary emitter; or (2) the OLEDfurther comprises a second organic layer disposed between the anode andthe cathode, where the second organic layer comprises a secondaryemitter. The phosphorescent emitter has a peak emission wavelength λmaxthat is ≥600 nm and ≤750 nm. The secondary emitter has a peak emissionwavelength λmax that is ≥750 nm. The first host has a lowest excitedstate triplet energy T1 that is at least 0.1 eV higher than that of thephosphorescent emitter.

In embodiments where condition (1) is true, the emissive layer comprisesat least three components including host material(s), the primaryphosphorescent emitter that is a first transition metal compound (M¹L¹_(n)), and the secondary NIR emitter comprised of one of the following:a second transition metal compound (M² _(L) ² _(n)), an organicfluorophore, or an organic doublet emitter. In the case of the secondaryNIR emitter being a second transition metal compound, the metal M² isselected from lanthanide elements. The disclosed OLED is usefulespecially for NIR application. The primary phosphorescent emitteracting as a sensitizer to the secondary NIR emitter refers to the factthat the primary phosphorescent emitter acts as an exciton formationsite to make use of the advantageous properties of a phosphorescent OLEDstack and allow for incorporation in a larger OLED based display. Wherethe primary phosphorescent emitter and the secondary NIR emitters areco-doped in an OLED's EML, the energy transfer from the primaryphosphorescent emitter sensitizer to the secondary NIR emitter proceedsthrough a Dexter energy transfer mechanism. Where the primaryphosphorescent emitter and the secondary NIR emitter are provided inseparate layers, the energy transfer from the primary phosphorescentemitter sensitizer to the secondary NIR emitter proceeds through aForster energy transfer mechanism and unwanted Dexter energy transfer isreduced.

In some embodiments of the OLED, the condition (1) is true, and thefirst organic layer is the only layer containing the secondary emitter.In some embodiments of the OLED, the condition (2) is true, and thesecond organic layer is the only layer containing the secondary emitter.

In some embodiments of the OLED, the condition (2) is true and thesecond organic layer further comprises a second host.

In some embodiments of the OLED, the secondary emitter has a peakabsorption wavelength and the difference between the peak emissionwavelength λ_(max) of the phosphorescent emitter and the peak absorptionwavelength λ_(max) of the secondary emitter is less than 200 nm.

In some embodiments of the OLED, the secondary emitter has a peakabsorption wavelength and the difference between the peak emissionwavelength λ_(max) of the phosphorescent emitter and the peak absorptionwavelength λ_(max) of the secondary emitter is less than 150 nm.

In some embodiments where the condition (2) is true, the first organiclayer and the second organic layer are separated by one or moreadditional organic layers. In some embodiments, at least one of theadditional organic layers can include a third host. In some embodiments,the first, second, and third hosts can be the same or different fromeach other.

In some embodiments where the condition (2) is true, and the firstorganic layer and the second organic layer are separated by one or moreadditional organic layers, at least one of the additional organic layerscomprises a charge transport material. In some embodiments, theseparation between the first organic layer and the second organic layeris ≥1 nm. In some embodiments, the separation between the first organiclayer and the second organic layer is ≥2 nm. In some embodiments, theseparation between the first organic layer and the second organic layeris ≥4 nm. FIG. 3 shows an example of such an OLED stack 300. In the OLEDstack 300, the first organic layer containing the primary emitter is theEML 1 and the second organic layer containing the secondary NIR emitteris the EML 2. The one or more additional organic layers, such as acharge transport material layer, separating the first organic layer andthe second organic layer is shown in the OLED stack 300 as TL layer of0-100 Å thick. In FIG. 3, the thicknesses of EML 1 and EML 2 are labeledas (0-500 Å) to show the maximum thickness of 500 Å. For example, in theembodiment where the OLED has both EML 1 (containing the primaryemitter) and EML 2 (containing the secondary NIR emitter), theirthicknesses would be something greater than 0 and up to 500 Å thick. Thethicknesses of the EIL (electron injection layer), ETL (electrontransport layer), BL (hole blocking layer), TL (charge transport layer),and EBL (electron blocking layer) are shown with a thickness range withthe bottom end of the range as “0” because these functional layers areoptional layers and in some embodiments of the OLED stack, one or moreof these layers do not exist. The HTL (hole transport layer) has athickness range of 50-1500 Å. the OLED further comprises a secondorganic layer comprising a secondary emitter.

In some embodiments of the OLED where the condition (1) is true,concentration of the phosphorescent emitter and concentration of thesecondary emitter in the first organic layer are different. In someembodiments, concentration of the phosphorescent emitter andconcentration of the secondary emitter in the first organic layer areeach ≤10 wt. %. In some embodiments, concentration of the phosphorescentemitter and concentration of the secondary emitter in the first organiclayer are each ≤5 wt. %. In some embodiments, concentration of thephosphorescent emitter and concentration of the secondary emitter in thefirst organic layer are each ≤3 wt. %. In some embodiments, an averageintermolecular distance between the phosphorescent emitter and thesecondary emitter is ≥8 Å. In some embodiments, an averageintermolecular distance between the phosphorescent emitter and thesecondary emitter is ≥10 Å. In some embodiments, an averageintermolecular distance between the phosphorescent emitter and thesecondary emitter is ≥12 Å.

In some embodiments of the OLED, the phosphorescent emitter has theformula M¹L¹ _(m); where M¹ is selected from the group consisting of Os,Ir, Pd, Pt, Cu, Ag, and Au; where can represent one or more ligands thatare the same or different; where each L¹ is independently monodentate ormultidentate; and where m represents a maximum possible number ofligands L¹ that can coordinate to M¹.

In some embodiments of the OLED, the secondary emitter has the formulaM²L² _(n), where M² is selected from the group consisting of thelanthanide metals, where L² represents one or more ligands that are thesame or different, where each L² is independently monodentate ormultidentate, and where n represents a maximum possible number of L²ligands that can coordinate to M².

In some embodiments of the OLED, the secondary emitter is a fluorescentemitter. In some embodiments, the secondary emitter is a thermallyactivated delayed fluorescence emitter. In some embodiments, thesecondary emitter contains an unpaired electron in its ground state.

In some embodiments of the OLED where the phosphorescent emitter has theformula M¹L¹ _(m) as defined above, M¹ is selected from the groupconsisting of Pt and Ir. In some embodiments, where the phosphorescentemitter has the formula M¹L¹ _(m) as defined above, the phosphorescentemitter has a formula of M¹(L_(A))_(x)(L_(B))_(y)(L_(C))_(z); whereinL_(A), L_(B), and L_(C) are each a bidentate ligand; and wherein x is 1,2, or 3; y is 0, 1, or 2; z is 0, 1, or 2; and x+y+z is the oxidationstate of the metal M.

In some embodiments of the OLED wherein the secondary emitter has theformula M²L² _(n) as defined above, the phosphorescent emitter has alowest triplet energy, T1, that is the same or higher than the energy ofthe emissive f-f transition, E_(f-f), of the secondary emitter. In someembodiments, M² is selected from the group consisting of Eu, Nd, Yb, andEr.

In some embodiments of the OLED where the phosphorescent emitter has aformula of M¹(L_(A))_(x)(L_(B))_(y)(L_(C))_(z) as defined above, thephosphorescent emitter has a formula selected from the group consistingof Ir(L_(A))₃, Ir(L_(A))(L_(B))₂, Ir(L_(A))₂(L_(B)), Ir(L_(A))2(L_(C)),and Ir(L_(A))(L_(B))(L_(C)); and wherein L_(A), L_(B), and L_(C)aredifferent from each other.

In some embodiments of the OLED where the phosphorescent emitter has aformula of M¹(L_(A))_(x)(L_(A))_(y)(L_(C))_(z) as defined above, thephosphorescent emitter has a formula of Pt(L_(A))(L_(B)); and whereinL_(A) and L_(B) can be same or different. In some embodiments, L_(A) andL_(B) are connected to form a tetradentate ligand. In some embodiments,L_(A) and L_(B) are connected at two places to form a macrocyclictetradentate ligand.

In some embodiments of the OLED where the phosphorescent emitter has aformula of M¹(L_(A))_(x)(L_(B))_(y)(L_(C))_(z) as defined above, L_(A),L_(B), and L_(C) are each independently selected from the groupconsisting of:

wherein each X¹ to X¹³ are independently selected from the groupconsisting of carbon and nitrogen; wherein X is selected from the groupconsisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂, CR′R″, SiR′R″, andGeR′R″; wherein R′ and R″ are optionally fused or joined to form a ring;wherein each R_(a), R_(b), R_(c), and R_(d) can represent from monosubstitution to the possible maximum number of substitution, or nosubstitution; wherein R′, R″, R_(a), R_(b), R_(c), and R_(d) are eachindependently a hydrogen or a substituent selected from the groupconsisting of deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, benzonitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; and wherein any twoadjacent substituents of R_(a), R_(b), R_(c), and R_(d) are optionallyfused or joined to form a ring or form a multidentate ligand. In someembodiments, L_(A) and L_(B) are each independently selected from thegroup consisting of:

In some embodiments of the OLED, where the secondary emitter is afluorescent emitter selected from the group consisting of:

wherein R¹ to R⁵ each independently represent from mono to maximumnumber of substitutions they can have, or no substitution;

wherein R¹ to R⁵ are each independently a hydrogen or a substituentselected from the group consisting of hydrogen, deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,sulfinyl, sulfonyl, phosphino, and combinations thereof; and

wherein at least one of R¹ to R⁵ is R.

In some embodiments of the OLED wherein the secondary emitter containsan unpaired electron in its ground state, the secondary emitter isselected from the group consisting of:

where R^(A), R^(B), R^(C), R^(D), and R^(E) each independently representmono to the maximum allowable substitution, or no substitution; andwherein R^(A), R^(B), R^(C), R^(D), and R^(E) are each independently ahydrogen or a substituent selected from the group consisting ofdeuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy,aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl,aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.

In some embodiments of the OLED, the first host comprises at least onechemical group selected from the group consisting of triphenylene,carbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene,azatriphenylene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran,and aza-dibenzoselenophene. In some embodiments, the first host isselected from the group consisting of:

and combinations thereof.

An OLED comprising an anode, a cathode, and a first organic layerdisposed between the anode and the cathode is disclosed. The firstorganic layer comprises a first metal complex M¹L¹ _(m) and a firsthost; wherein one of the following conditions is true:

(1) the first organic layer further comprises a second metal complexM²L² _(n); or

(2) the OLED device further comprises a second organic layer disposedbetween the anode and the cathode, where the second organic layercomprises a second metal complex M²L² _(n);

wherein M¹ is selected from the group consisting of Os, Ir, Pd, Pt, Cu,Ag, and Au;wherein M² is selected from the group consisting of the lanthanidemetals;wherein L¹ and L² are each independently monodentate or multidentateligands and can represent multiple ligands that are the same ordifferent;wherein m represents the maximum possible number of ligands that cancoordinate to M¹;wherein n represents the maximum possible number of ligands L² that cancoordinate to M²;wherein the first host has a lowest triplet energy T1 that is the sameor higher than the lowest triplet energy T1 of the first metal complexM¹L¹ _(m); andwherein the first metal complex M¹L¹ _(m) has a lowest triplet energy,T1, that is the same or higher than the energy of the emissive f-ftransition, E_(f-f), of the second metal complex M²L² _(n).

In some embodiments of the OLED, the condition (1) is true, and thefirst organic layer is the only layer containing M²L² _(n). In someembodiments of the OLED, the condition (2) is true, and the secondorganic layer is the only layer containing M²L² _(n). In someembodiments of the OLED where the condition (2) is true, the secondorganic layer further comprises a host.

In some embodiments of the OLED, M¹ is selected from the groupconsisting of Pt and Ir. In some embodiments of the OLED, M² is selectedfrom the group consisting of Eu, Nd, Yb, and Er. In some embodiments ofthe OLED, at least one of the ligands L² has a lowest triplet energy T1that is the same or lower than the lowest triplet energy T1 of the firstmetal complex M¹L¹ _(m). In some embodiments of the OLED, at least oneof the ligands L² has a lowest triplet energy T1 that is the same orhigher than the lowest triplet energy T1 of the first metal complex M¹L¹_(m).

In some embodiments of the OLED, M² is Eu. In some embodiments of theOLED, M² is Yb. In some embodiments of the OLED, M² is Nd. In someembodiments of the OLED, M² is Er.

In some embodiments of the OLED, the first metal complex M¹L¹ _(m) has aformula of M¹(L_(A))_(x)(L_(B))_(y)(L_(C))_(z) wherein L_(A), L_(B) andL_(C) are each a bidentate ligand; and wherein x is 1, 2, or 3; y is 0,1, or 2; z is 0, 1, or 2; and x+y+z is the oxidation state of the metalM. In some embodiments, the first metal complex M¹L¹ _(m) has a formulaselected from the group consisting of Ir(L_(A))₃, Ir(L_(A))(L_(B))₂,Ir(L_(A))₂(L_(B)), Ir(L_(A))₂(L_(C)), and Ir(L_(A))(L_(B))(L_(C)); andwherein L_(A), L_(B), and L_(C) are different from each other. In someembodiments, the first metal complex M¹L¹ _(m) has a formula ofPt(L_(A))(L_(B)); and wherein L_(A) and L_(B) can be same or different.

In some embodiments of the OLED where the first metal complex M¹L¹ _(m),has a formula of Pt(L_(A))(L_(B)), and wherein L_(A) and L_(B) can besame or different, L_(A) and L_(B) are connected to form a tetradentateligand. In some embodiments, L_(A) and L_(B) are connected at two placesto form a macrocyclic tetradentate ligand.

In some embodiments of the OLED wherein the first metal complex M¹L¹_(m) has a formula selected from the group consisting of Ir(L_(A))3,Ir(L_(A))(L_(B))₂, Ir(L_(A))₂(L_(B)), Ir(L_(A))₂(L_(C)), andIr(L_(A))(L_(B))(L_(C)); and wherein L_(A), L_(B), and L_(C) aredifferent from each other, L_(A), L_(B), and L_(C) are eachindependently selected from the group consisting of:

wherein each X¹ to X¹³ are independently selected from the groupconsisting of carbon and nitrogen; wherein X is selected from the groupconsisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂,CR′R″, SiR′R″, andGeR′R″; wherein R′ and R″ are optionally fused or joined to form a ring;wherein each R_(a), R_(b), R_(c), and R_(d) can represent from monosubstitution to the possible maximum number of substitution, or nosubstitution; wherein R′, R″, R_(a), R_(b), R_(c), and R_(d) are eachindependently a hydrogen or a substituent selected from the groupconsisting of deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, benzonitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; and wherein any twoadjacent substituents of R_(a), R_(b), R_(c), and R_(d) are optionallyfused or joined to form a ring or form a multidentate ligand. In someembodiments, L_(A) and L_(B) are each independently selected from thegroup consisting of:

In some embodiments of the OLED, the second metal complex M²L² _(n) isselected from the following group (A) consisting of:

wherein rings A, B, and C are each independently a 5-membered or6-membered carbocyclic or heterocyclic ring; wherein R^(A), R^(B),R^(C), R^(D), R^(E), and R^(F) can represent mono to the maximumpossible substitution, or no substitution; wherein R^(A), R^(B), R^(C),R^(D), R^(E), and R^(F) are each independently a hydrogen or asubstituent selected from the group consisting of deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, benzonitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof; and wherein L³ and L⁴ are each independently selected fromdirect bond, BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, GeRR′,alkyl, cycloalkyl, and combinations thereof.

In some embodiments of the OLED, the second metal complex M²L² _(n) isselected from the group consisting of:

Compounds 1 through 4 having the following structure

wherein in Compound 1, M² = Nd, in Compound 2, M² = Eu, in Compound 3,M² = Yb, and in Compound 4, M² = Er, Compounds 5 through 8 having thefollowing structure

wherein in Compound 5, M² = Nd, in Compound 6, M² = Eu, in Compound 7,M² = Yb, and in Compound 8, M² = Er, Compounds 9 through 12 having thefollowing structure

wherein in Compound 9, M2 = Nd, in Compound 10, M2 = Eu, in Compound 11,M2 = Yb, and in Compound 12, M2 = Er, Compounds 13 through 16 having thefollowing structure

wherein in Compound 13, M² = Nd, in Compound 14, M² = Eu, in Compound15, M² = Yb, and in Compound 16, M² = Er, Compounds 17 through 20 havingthe following structure

wherein in Compound 17, M² = Nd, in Compound 18, M² = Eu, in Compound19, M² = Yb, and in Compound 20, M² = Er, Compounds 21 through 24 havingthe following structure

wherein in Compound 21, M² = Nd, in Compound 22, M² = Eu, in Compound23, M² = Yb, and in Compound 24, M² = Er, Compounds 25 through 28 havingthe following structure

wherein in Compound 25, M² = Nd, in Compound 26, M² = Eu, in Compound27, M² = Yb, and in Compound 28, M² = Er, Compounds 29 through 32 havingthe following structure

wherein in Compound 29, M² = Nd, in Compound 30, M² = Eu, in Compound31, M² = Yb, and in Compound 32, M² = Er, Compounds 33 through 36 havingthe following structure

wherein in Compound 33, M² = Nd, in Compound 34, M² = Eu, in Compound35, M² = Yb, and in Compound 36, M² = Er, Compounds 37 through 40 havingthe following structure

wherein in Compound 37, M² = Nd, in Compound 38, M² = Eu, in Compound39, M² = Yb, and in Compound 40, M² = Er, Compounds 41 through 44 havingthe following structure

wherein in Compound 41, M² = Nd, in Compound 42, M² = Eu, in Compound43, M² = Yb, and in Compound 44, M² = Er, Compounds 45 through 48 havingthe following structure

wherein in Compound 45, M² = Nd, in Compound 46, M² = Eu, in Compound47, M² = Yb, and in Compound 48, M² = Er, Compounds 49 through 52 havingthe following structure

wherein in Compound 49, M² = Nd, in Compound 50, M² = Eu, in Compound51, M² = Yb, and in Compound 52, M² = Er, Compounds 53 through 54 havingthe following structure

wherein in Compound 53, M² = Nd, in Compound 54, M² = Eu, in Compound55, M² = Yb, and in Compound 56, M² = Er, Compounds 57 through 60 havingthe following structure

wherein in Compound 57, M2 = Nd, in Compound 58, M2 = Eu, in Compound59, M2 = Yb, and in Compound 60, M2 = Er, Compounds 61 through 64 havingthe following structure

wherein in Compound 61, M² = Nd, in Compound 62, M² = Eu, in Compound63, M² = Yb, and in Compound 64, M² = Er, Compounds 65 through 68 havingthe following structure

wherein in Compound 65, M² = Nd, in Compound 66, M² = Eu, in Compound67, M² = Yb, and in Compound 68, M² = Er, Compounds 69 through 72 havingthe following structure

wherein in Compound 69, M² = Nd, in Compound 70, M² = Eu, in Compound71, M² = Yb, and in Compound 72, M² = Er.

In some embodiments of the OLED, the first host comprises at least onechemical group selected from the group consisting of triphenylene,carbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene,azatriphenylene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran,and aza-dibenzoselenophene.

In some embodiments of the OLED, the first host is selected from thegroup consisting of:

and combinations thereof.

The use of a phosphorescent emitter to sensitize another secondaryemitter such as a fluorescent or lanthanide emitter offers a method ofobtaining higher efficiency from the secondary emitter while retainingits emission properties. However, we predict a particular benefit forthe application of this device structure in the near-infrared emissionregion. Specific to the near-infrared, the secondary emitter allows foran increase in device efficiency due to the shorter transient lifetimeoffered by these emitters. As the energy gap law predicts an exponentialincrease in non-radiative rate with decreasing excited state to groundstate (emission) energy gap, efficient NIR emission requires a very fastemissive rate to compete with the faster non-radiative decay in thisregime. As such, the use of secondary emitters with faster emissiverates (e.g. fluorophores) is expected to result in higher efficiencythan both an all phosphorescent device, which suffers from long excitedstate lifetimes, and an all fluorescent device, which suffers from loweremission quantum yield due to wasted triplet excitons.

Standard measurement of peak wavelength (λmax) is as follows:photoluminescence is measured by photoexcitation of a thin film sampleof the emitter doped at 1% (wt. %) in an inert Poly(methyl methacrylate)matrix.

In some embodiments, the OLED has one or more characteristics selectedfrom the group consisting of being flexible, being rollable, beingfoldable, being stretchable, and being curved. In some embodiments, theOLED is transparent or semi-transparent. In some embodiments, the OLEDfurther comprises a layer comprising carbon nanotubes.

In some embodiments, the OLED further comprises a layer comprising adelayed fluorescent emitter. In some embodiments, the OLED comprises aRGB pixel arrangement or white plus color filter pixel arrangement. Insome embodiments, the OLED is a mobile device, a hand held device, or awearable device. In some embodiments, the OLED is a display panel havingless than 10 inch diagonal or 50 square inch area. In some embodiments,the OLED is a display panel having at least 10 inch diagonal or 50square inch area. In some embodiments, the OLED is a lighting panel.

An emissive region in an OLED is also disclosed where the emissiveregion comprising the first organic layer described herein.

In some embodiments, the compound can be an emissive dopant. In someembodiments, the compound can produce emissions via phosphorescence,fluorescence, thermally activated delayed fluorescence, i.e., TADF (alsoreferred to as E-type delayed fluorescence; see, e.g., U.S. applicationSer. No. 15/700,352, which is hereby incorporated by reference in itsentirety), triplet-triplet annihilation, or combinations of theseprocesses.

According to another aspect, a formulation comprising the compounddescribed herein is also disclosed.

The OLED disclosed herein can be incorporated into one or more of aconsumer product, an electronic component module, and a lighting panel.The organic layer can be an emissive layer and the compound can be anemissive dopant in some embodiments, while the compound can be anon-emissive dopant in other embodiments.

The organic layer can also include a host. In some embodiments, two ormore hosts are preferred. In some embodiments, the hosts used may be a)bipolar, b) electron transporting, c) hole transporting or d) wide bandgap materials that play little role in charge transport. In someembodiments, the host can include a metal complex. The host can be atriphenylene containing benzo-fused thiophene or benzo-fused furan. Anysubstituent in the host can be an unfused substituent independentlyselected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1),OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1),C≡C—C_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, and C_(n)H_(2n)—Ar₁, or the host has nosubstitutions. In the preceding substituents n can range from 1 to 10;and Ar₁ and Ar₂ can be independently selected from the group consistingof benzene, biphenyl, naphthalene, triphenylene, carbazole, andheteroaromatic analogs thereof. The host can be an inorganic compound.For example a Zn containing inorganic material e.g. ZnS.

The host can be a compound comprising at least one chemical groupselected from the group consisting of triphenylene, carbazole,dibenzothiophene, dibenzofuran, dibenzoselenophene, azatriphenylene,azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, andaza-dibenzoselenophene. The host can include a metal complex. The hostcan be, but is not limited to, a specific compound selected from thegroup consisting of:

and combinations thereof.Additional information on possible hosts is provided below.

In yet another aspect of the present disclosure, a formulation thatcomprises the novel compound disclosed herein is described. Theformulation can include one or more components selected from the groupconsisting of a solvent, a host, a hole injection material, holetransport material, electron blocking material, hole blocking material,and an electron transport material, disclosed herein.

Combination With Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

Conductivity Dopants:

A charge transport layer can be doped with conductivity dopants tosubstantially alter its density of charge carriers, which will in turnalter its conductivity. The conductivity is increased by generatingcharge carriers in the matrix material, and depending on the type ofdopant, a change in the Fermi level of the semiconductor may also beachieved. Hole-transporting layer can be doped by p-type conductivitydopants and n-type conductivity dopants are used in theelectron-transporting layer.

Non-limiting examples of the conductivity dopants that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:EP01617493, EP01968131, EP2020694, EP2684932, US20050139810,US20070160905, US20090167167, US2010288362, WO06081780, WO2009003455,WO2009008277, WO2009011327, WO2014009310, US2007252140, US2015060804,US20150123047, and US2012146012.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but are not limited to: aphthalocyanine or porphyrin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and silane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting of aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, and azulene; the group consistingof aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and the group consisting of 2 to 10 cyclic structural units which aregroups of the same type or different types selected from the aromatichydrocarbon cyclic group and the aromatic heterocyclic group and arebonded to each other directly or via at least one of oxygen atom,nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom,chain structural unit and the aliphatic cyclic group. Each Ar may beunsubstituted or may be substituted by a substituent selected from thegroup consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylicacids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH)or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but are notlimited to the following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40;(Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independentlyselected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and k′+k″ is the maximum number of ligands thatmay be attached to the metal.

In one aspect, (Y¹⁰¹-V¹⁰²) is a 2-phenylpyridine derivative. In anotheraspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met isselected from Ir, Pt, Os, and Zn. In a further aspect, the metal complexhas a smallest oxidation potential in solution vs. Fc⁺/Fc couple lessthan about 0.6 V.

Non-limiting examples of the HIL and HTL materials that may be used inan OLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:CN102702075, DE102012005215, EP01624500, EP01698613, EP01806334,EP01930964, EP01972613, EP01997799, EP02011790, EP02055700, EP02055701,EP1725079, EP2085382, EP2660300, EP650955, JP07-073529, JP2005112765,JP2007091719, JP2008021687, JP2014-009196, KR20110088898, KR20130077473,TW201139402, US06517957, US20020158242, US20030162053, US20050123751,US20060182993, US20060240279, US20070145888, US20070181874,US20070278938, US20080014464, US20080091025, US20080106190,US20080124572, US20080145707, US20080220265, US20080233434,US20080303417, US2008107919, US20090115320, US20090167161, US2009066235,US2011007385, US20110163302, US2011240968, US2011278551, US2012205642,US2013241401, US20140117329, US2014183517, U.S. Pat. Nos. 5,061,569,5,639,914, WO05075451, WO07125714, WO08023550, WO08023759, WO2009145016,WO2010061824, WO2011075644, WO2012177006, WO2013018530, WO2013039073,WO2013087142, WO2013118812, WO2013120577, WO2013157367, WO2013175747,WO2014002873, WO2014015935, WO2014015937, WO2014030872, WO2014030921,

WO2014034791, WO2014104514, WO2014157018.

EBL:

An electron blocking layer (EBL) may be used to reduce the number ofelectrons and/or excitons that leave the emissive layer. The presence ofsuch a blocking layer in a device may result in substantially higherefficiencies, and/or longer lifetime, as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the EBLmaterial has a higher LUMO (closer to the vacuum level) and/or highertriplet energy than the emitter closest to the EBL interface. In someembodiments, the EBL material has a higher LUMO (closer to the vacuumlevel) and/or higher triplet energy than one or more of the hostsclosest to the EBL interface. In one aspect, the compound used in EBLcontains the same molecule or the same functional groups used as one ofthe hosts described below.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. Any host material may be used with any dopant so long as thetriplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴are independently selected from C, N, O, P, and S; L¹⁰¹ is an anotherligand; k′ is an integer value from 1 to the maximum number of ligandsthat may be attached to the metal; and k′+k″ is the maximum number ofligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms Oand N.

In another aspect, Met is selected from Ir and Pt. In a further aspect,(Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of other organic compounds used as host are selected from thegroup consisting of aromatic hydrocarbon cyclic compounds such asbenzene, biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene,anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene,perylene, and azulene; the group consisting of aromatic heterocycliccompounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene,furan, thiophene, benzofuran, benzothiophene, benzoselenophene,carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole,imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole,dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine,triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole,indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole,quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline,naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine,phenothiazine, phenoxazine, benzofuropyridine, furodipyridine,benzothienopyridine, thienodipyridine, benzoselenophenopyridine, andselenophenodipyridine; and the group consisting of 2 to 10 cyclicstructural units which are groups of the same type or different typesselected from the aromatic hydrocarbon cyclic group and the aromaticheterocyclic group and are bonded to each other directly or via at leastone of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorusatom, boron atom, chain structural unit and the aliphatic cyclic group.Each option within each group may be unsubstituted or may be substitutedby a substituent selected from the group consisting of deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.

In one aspect, the host compound contains at least one of the followinggroups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether,ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof, and when it is aryl or heteroaryl, it has thesimilar definition as Ar's mentioned above. k is an integer from 0 to 20or 1 to 20. X¹⁰¹ to X¹⁰⁸ are independently selected from C (includingCH) or N. Z¹⁰¹ and Z¹⁰² are independently selected from NR¹⁰¹, O, or S.

Non-limiting examples of the host materials that may be used in an OLEDin combination with materials disclosed herein are exemplified belowtogether with references that disclose those materials: EP2034538,EP2034538A, EP2757608, JP2007254297, KR20100079458, KR20120088644,KR20120129733, KR20130115564, TW201329200, US20030175553, US20050238919,US20060280965, US20090017330, US20090030202, US20090167162,US20090302743, US20090309488, US20100012931, US20100084966,US20100187984, US2010187984, US2012075273, US2012126221, US2013009543,US2013105787, US2013175519, US2014001446, US20140183503, US20140225088,US2014034914, U.S. Pat. No. 7,154,114, WO2001039234, WO2004093207,WO2005014551, WO2005089025, WO2006072002, WO2006114966, WO2007063754,WO2008056746, WO2009003898, WO2009021126, WO2009063833, WO2009066778,WO2009066779, WO2009086028, WO2010056066, WO2010107244, WO2011081423,WO2011081431, WO2011086863, WO2012128298, WO2012133644, WO2012133649,WO2013024872, WO2013035275, WO2013081315, WO2013191404, WO2014142472,US20170263869, US20160163995, U.S. Pat. No. 9,466,803,

Additional Emitters:

One or more additional emitter dopants may be used in conjunction withthe compound of the present disclosure. Examples of the additionalemitter dopants are not particularly limited, and any compounds may beused as long as the compounds are typically used as emitter materials.Examples of suitable emitter materials include, but are not limited to,compounds which can produce emissions via phosphorescence, fluorescence,thermally activated delayed fluorescence, i.e., TADF (also referred toas E-type delayed fluorescence), triplet-triplet annihilation, orcombinations of these processes.

Non-limiting examples of the emitter materials that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:CN103694277, CN1696137, EB01238981, EP01239526, EP01961743, EP1239526,EP1244155, EP1642951, EP1647554, EP1841834, EP1841834B, EP2062907,EP2730583, JP2012074444, JP2013110263, JP4478555, KR1020090133652,KR20120032054, KR20130043460, TW201332980, US06699599, US06916554,US20010019782, US20020034656, US20030068526, US20030072964,US20030138657, US20050123788, US20050244673, US2005123791, US2005260449,US20060008670, US20060065890, US20060127696, US20060134459,US20060134462, US20060202194, US20060251923, US20070034863,US20070087321, US20070103060, US20070111026, US20070190359,US20070231600, US2007034863, US2007104979, US2007104980, US2007138437,US2007224450, US2007278936, US20080020237, US20080233410, US20080261076,US20080297033, US200805851, US2008161567, US2008210930, US20090039776,US20090108737, US20090115322, US20090179555, US2009085476, US2009104472,US20100090591, US20100148663, US20100244004, US20100295032,US2010102716, US2010105902, US2010244004, US2010270916, US20110057559,US20110108822, US20110204333, US2011215710, US2011227049, US2011285275,US2012292601, US20130146848, US2013033172, US2013165653, US2013181190,US2013334521, US20140246656, US2014103305, U.S. Pat. Nos. 6,303,238,6,413,656, 6,653,654, 6,670,645, 6,687,266, 6,835,469, 6,921,915,7,279,704, 7,332,232, 7,378,162, 7,534,505, 7,675,228, 7,728,137,7,740,957, 7,759,489, 7,951,947, 8,067,099, 8,592,586, 8,871,361,WO06081973, WO06121811, WO07018067, WO07108362, WO07115970, WO07115981,WO08035571, WO2002015645, WO2003040257, WO2005019373, WO2006056418,WO2008054584, WO2008078800, WO2008096609, WO2008101842, WO2009000673,WO2009050281, WO2009100991, WO2010028151, WO2010054731, WO2010086089,WO2010118029, WO2011044988, WO2011051404, WO2011107491, WO2012020327,WO2012163471, WO2013094620, WO2013107487, WO2013174471, WO2014007565,WO2014008982, WO2014023377, WO2014024131, WO2014031977, WO2014038456,WO2014112450.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies and/or longer lifetime as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the HBLmaterial has a lower HOMO (further from the vacuum level) and/or highertriplet energy than the emitter closest to the HBL interface. In someembodiments, the HBL material has a lower HOMO (further from the vacuumlevel) and/or higher triplet energy than one or more of the hostsclosest to the HBL interface.

In one aspect, compound used in HBL contains the same molecule or thesame functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ isan integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether,ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof, when it is aryl or heteroaryl, it has the similardefinition as Ar's mentioned above. Ar¹ to Ar³ has the similardefinition as Ar's mentioned above. k is an integer from 1 to 20. X¹⁰¹to X¹⁰⁸ is selected from C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinatedto atoms O, N or N, N; L¹⁰¹ is another ligand; k′ is an integer valuefrom 1 to the maximum number of ligands that may be attached to themetal.

Non-limiting examples of the ETL materials that may be used in an OLEDin combination with materials disclosed herein are exemplified belowtogether with references that disclose those materials: CN103508940,EP01602648, EP01734038, EP01956007, JP2004-022334, JP2005149918,JP2005-268199, KR0117693, KR20130108183, US20040036077, US20070104977,US2007018155, US20090101870, US20090115316, US20090140637,US20090179554, US2009218940, US2010108990, US2011156017, US2011210320,US2012193612, US2012214993, US2014014925, US2014014927, US20140284580,U.S. Pat. Nos. 6,656,612, 8,415,031, WO2003060956, WO2007111263,WO2009148269, WO2010067894, WO2010072300, WO2011074770, WO2011105373,WO2013079217, WO2013145667, WO2013180376, WO2014104499, WO2014104535,

Charge Generation Layer (CGL)

In tandem or stacked OLEDs, the CGL plays an essential role in theperformance, which is composed of an n-doped layer and a p-doped layerfor injection of electrons and holes, respectively. Electrons and holesare supplied from the CGL and electrodes. The consumed electrons andholes in the CGL are refilled by the electrons and holes injected fromthe cathode and anode, respectively; then, the bipolar currents reach asteady state gradually. Typical CGL materials include n and pconductivity dopants used in the transport layers.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated. Thus, anyspecifically listed substituent, such as, without limitation, methyl,phenyl, pyridyl, etc. may be undeuterated, partially deuterated, andfully deuterated versions thereof. Similarly, classes of substituentssuch as, without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc.also may be undeuterated, partially deuterated, and fully deuteratedversions thereof.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1. An organic light emitting device (OLED) comprising: an anode; acathode; a first organic layer, disposed between the anode and thecathode; wherein the first organic layer comprises a primaryphosphorescent emitter and a first host; wherein one of the followingconditions is true: (1) the first organic layer further comprises asecondary emitter; or (2) the OLED device further comprises a secondorganic layer disposed between the anode and the cathode, wherein thesecond organic layer comprises a secondary emitter; wherein the primaryphosphorescent emitter has a peak emission wavelength λmax that is ≥600nm and ≤750 nm; wherein the secondary emitter has a peak emissionwavelength λmax that is ≥750 nm; and wherein the first host has a lowestexcited state triplet energy T1 that is at least 0.1 eV higher than thatof the primary phosphorescent emitter.
 2. The OLED of claim 1, whereinthe condition (1) is true, and the first organic layer is the only layercontaining the secondary emitter.
 3. The OLED of claim 1, wherein thecondition (2) is true, and the second organic layer is the only layercontaining the secondary emitter.
 4. (canceled)
 5. The OLED of claim 1,wherein the secondary emitter has a peak absorption wavelength and thedifference between the peak emission wavelength λ_(max) of the primaryphosphorescent emitter and the peak absorption wavelength λ_(max) of thesecondary emitter is less than 200 nm. 6.-8. (canceled)
 9. The OLED ofclaim 1, wherein the first organic layer and the second organic layerare separated by one or more additional organic layers. 10.-11.(canceled)
 12. The OLED of claim 9, wherein the separation between thefirst organic layer and the second organic layer is ≥1 nm. 13.-14.(canceled)
 15. The OLED of claim 1, wherein the condition (1) is true,and wherein the concentration of the primary phosphorescent emitter andconcentration of the secondary emitter in the first organic layer aredifferent.
 16. The OLED of claim 1, wherein the condition (1) is true,and wherein the concentration of the primary phosphorescent emitter andthe concentration of the secondary emitter in the first organic layerare each ≤10 wt. %. 17.-20. (canceled)
 21. The OLED of claim 1, whereinthe condition (1) is true, and wherein an average intermoleculardistance between the primary phosphorescent emitter and the secondaryemitter is ≥8 Å. 22.-23. (canceled)
 24. The OLED of claim 1, wherein theprimary phosphorescent emitter has the formula M¹L¹ _(m); wherein M¹ isselected from the group consisting of Os, Ir, Pd, Pt, Cu, Ag, and Au;wherein L¹ can represent one or more ligands that are the same ordifferent; wherein each L¹ is independently monodentate or multidentate;and wherein m represents a maximum possible number of ligands L¹ thatcan coordinate to M¹.
 25. The OLED of claim 1, wherein the secondaryemitter has the formula M²L² _(n); wherein M² is selected from the groupconsisting of the lanthanide metals; wherein L² represents one or moreligands that are the same or different; wherein each L² is independentlymonodentate or multidentate; and wherein n represents a maximum possiblenumber of L² ligands that can coordinate to M².
 26. The OLED of claim 1,wherein the secondary emitter is selected from a group consisting of afluorescent emitter, a thermally activated delayed fluorescence emitter,and an emitter containing an unpaired electron in its ground state.27.-29. (canceled)
 30. The OLED of claim 24, wherein the phosphorescentemitter has a formula of M¹(L_(A))_(x)(L_(B))_(y)(L_(C))_(z); whereinL_(A), L_(B) and L_(C) are each a bidentate ligand; and wherein x is 1,2, or 3; y is 0, 1, or 2; z is 0, 1, or 2; and x+y+z is the oxidationstate of the metal M.
 31. The OLED of claim 25, wherein thephosphorescent emitter has a lowest triplet energy T1 that is the sameor higher than the energy of the emissive f-f transition E_(f-f) of thesecondary emitter.
 32. The OLED of claim 25, wherein M² is selected fromthe group consisting of Eu, Nd, Yb, and Er. 33.-36. (canceled)
 37. TheOLED of claim 30, wherein L_(A), L_(B), and L_(C) are each independentlyselected from the group consisting of:

wherein each X¹ to X¹³ are independently selected from the groupconsisting of carbon and nitrogen; wherein X is selected from the groupconsisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂, CR′R″, SiR′R″, andGeR′R″; wherein R′ and R″ are optionally fused or joined to form a ring;wherein each R_(a), R_(b), R_(c), and R_(d) can represent from monosubstitution to the possible maximum number of substitution, or nosubstitution; wherein R′, R″, R_(a), R_(b), R_(c), and R_(d) are eachindependently a hydrogen or a substituent selected from the groupconsisting of deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, benzonitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; and wherein any twoadjacent substituents of R_(a), R_(b), R_(c), and R_(d) are optionallyfused or joined to form a ring or form a multidentate ligand. 38.(canceled)
 39. The OLED of claim 26, wherein the fluorescent emitter isselected from the group consisting of:

wherein R¹ to R⁵ each independently represent from mono to maximumnumber of substitutions they can have, or no substitution; wherein R¹ toR⁵ are each independently a hydrogen or a substituent selected from thegroup consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; and wherein at least oneof R¹ to R⁵ is R.
 40. The OLED of claim 26, wherein the secondaryemitter is selected from the group consisting of:

wherein R^(A), R^(B), R^(C), R^(D), and R^(E) each independentlyrepresent mono to the maximum allowable substitution, or nosubstitution; and wherein R^(A), R^(B), R^(C), R^(D), and R^(E) are eachindependently selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof. 41.-61. (canceled)
 62. The OLED of claim 25, wherein the secondmetal complex M²L² _(n) is selected from the group consisting of:

wherein rings A, B, and C are each independently a 5-membered or6-membered carbocyclic or heterocyclic ring; wherein R^(A), R^(B),R^(C), R^(D), R^(E), and R_(F) can represent mono to the maximumpossible substitution, or no substitution; wherein R^(A), R^(B), R^(C),R^(D), R^(E), and R_(F) are each independently a hydrogen or asubstituent selected from the group consisting of deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, benzonitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof; and wherein L³ and L⁴ are each independently selected fromdirect bond, BR, NR, PR, O, S, Se, C=O, S═O, SO2,CRR′, SiRR′, GeRR′,alkyl, cycloalkyl, and combinations thereof. 63.-65. (canceled)
 66. Aconsumer product comprising an OLED comprising: an anode; a cathode; anda first organic layer disposed between the anode and the cathode;wherein the first organic layer comprises a primary phosphorescentemitter and a first host; wherein one of the following conditions istrue: (1) the first organic layer further comprises a secondary emitter;or (2) the OLED device further comprises a second organic layer disposedbetween the anode and the cathode, wherein the second organic layercomprises a secondary emitter; wherein the primary phosphorescentemitter has a peak emission wavelength λmax that is ≥600 nm and ≤750 nm;wherein the secondary emitter has a peak emission wavelength λmax thatis ≥750 nm; and wherein the first host has a lowest excited statetriplet energy T1 that is at least 0.1 eV higher than that of theprimary phosphorescent emitter, wherein the consumer product is one of aflat panel display, a computer monitor, a medical monitors television, abillboard, a light for interior or exterior illumination and/orsignaling, a heads-up display, a fully or partially transparent display,a flexible display, a laser printer, a telephone, a cell phone, tablet,a phablet, a personal digital assistant (PDA), a wearable OLED, a laptopcomputer, a digital camera, a camcorder, a viewfinder, a micro-display,a 3-D display, a virtual reality or augmented reality display, avehicle, a large area wall, a theater or stadium screen, a light therapydevice, or a sign.
 67. (canceled)